Method and apparatus for construction of compact optical nodes using wavelength equalizing arrays

ABSTRACT

Example embodiments of the present invention relate to An optical node comprising of at least two optical degrees; a plurality of directionless add/drop ports; and at least one wavelength equalizing array, wherein the at least one wavelength equalizing array is used to both select wavelengths for each degree, and to perform directionless steering for the add/drop ports.

RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.13/924,542, filed Jun. 22, 2013. The specification of the presentinvention is substantially the same as that of the parent application.The “Related Application” paragraph has been revised to include aspecific reference to the parent application. The specification of thepresent invention contains no new subject matter.

BACKGROUND

As the bandwidth needs of end customers increases, larger amounts ofoptical bandwidth will need to be manipulated closer to the endcustomers. A new breed of optical processing equipment will be needed toprovide high levels of optical bandwidth manipulation at the lower costpoints demanded at the networks closest to the end customers. This newbreed of optical processing equipment will require new levels of opticalsignal processing integration.

SUMMARY

A method and corresponding apparatus in an example embodiment of thepresent invention relates to providing a means of manipulating opticalsignals at the lowest possible cost points. The example embodimentincludes a compact light processing apparatus—utilizing wavelengthequalizing arrays—whose level of equipment redundancy matches theeconomics associated with the location of the apparatus within providernetworks.

According to an embodiment of the present invention, there is providedan optical node comprising of at least two optical degrees, a pluralityof directionless add/drop ports, and at least one wavelength equalizingarray; wherein the at least one wavelength equalizing array is used toboth select wavelengths for each optical degree and to performdirectionless steering for the plurality of directionless add/dropports. According to another embodiment of the invention, an apparatusreferred to as a ROADM circuit pack is described. The ROADM circuit packis comprised of a least two optical degrees and a port common to the atleast two optical degrees, wherein the common port is connectable to aplurality of directionless add/drop ports, and wherein wavelengths fromthe common port may be directed to any of the at least two degreesresiding on the circuit pack. The ROADM circuit pack may additionallycomprise of at least one wavelength equalizing array, wherein the atleast one wavelength equalizing array is used to both select wavelengthsfor each degree, and to perform directionless steering of wavelengths toand from the plurality of directionless add/drop ports. The at least oneequalizing array may further be utilized to aid in providing additionalfunctionality to the ROADM circuit pack, including, but not limited to,a channel monitoring function and the functionality of at least oneembedded transponder.

The invention also provides a method for constructing an optical nodeutilizing a wavelength equalizing array. The method comprises ofallocating a first set of wavelength equalizers for selection of a firstset of wavelengths for transmission from a first optical degree, andallocating at least a second set of wavelength equalizers for selectionof at least a second set of wavelengths for transmission from at least asecond optical degree; wherein the number of optical degrees comprisingthe node is used to determine the number of wavelength equalizersassigned to each set. The method further includes allocating anadditional set of wavelength equalizers for selection of an additionalset of wavelengths for transmission from a common port connectable to aplurality of directionless add/drop ports. The method may additionallyinclude allocating wavelength equalizers for a channel monitoringfunction and for an embedded transponder function.

The present invention provides various advantages over conventionalmethods and apparatus for construction of optical nodes. The advantagesarise from the use of a single wavelength equalizing array that allowsfor the construction of highly integrated optical nodes.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be apparent from the following more particulardescription of example embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingembodiments of the present invention.

FIG. 1 is an illustration of a wavelength equalizer, also often referredto as a wavelength blocker.

FIG. 2 is an illustration of a wavelength equalizing array containingsix wavelength equalizers.

FIG. 3 is an illustration of three wavelength equalizing arrays; onecontaining ten wavelength equalizers, one containing twelve wavelengthequalizers, and one containing u wavelength equalizers.

FIG. 4 is an illustration of a first embodiment of a wavelengthequalizing array containing six wavelength equalizers that can beconfigured to be any combination of 1 by 1 wavelength selective switchesor 2 by 1 wavelength selective switches.

FIG. 5 is an illustration of a second embodiment of a wavelengthequalizing array containing six wavelength equalizers that can beconfigured to be any combination of 1 by 1 wavelength selective switchesor 2 by 1 wavelength selective switches.

FIG. 6 is an illustration of a wavelength equalizing array containingten wavelength equalizers that can be configured to be any combinationof 1 by 1 wavelength selective switches or 2 by 1 wavelength selectiveswitches.

FIG. 7 is an illustration of a wavelength equalizing array containingsix wavelength equalizers that can be configured to be any combinationof 1 by 1 wavelength selective switches, 2 by 1 wavelength selectiveswitches, or 3 by 1 wavelength selective switches.

FIG. 8 is an illustration of a wavelength equalizing array containingtwelve wavelength equalizers that can be configured to be anycombination of 1 by 1 wavelength selective switches, 2 by 1 wavelengthselective switches, or 3 by 1 wavelength selective switches.

FIG. 9 is an illustration of an optical node comprising of a two degreeROADM on a circuit pack with an external multiplexer/de-multiplexercircuit pack.

FIG. 10 is an illustration of an optical node comprising of a two degreeROADM on a circuit pack utilizing a wavelength equalizing arraycontaining six wavelength equalizers, with an externalmultiplexer/de-multiplexer circuit pack.

FIG. 11 is an illustration of an alternative embodiment optical nodecomprising of a two degree ROADM on a circuit pack utilizing awavelength equalizing array containing six wavelength equalizers, withan external multiplexer/de-multiplexer circuit pack.

FIG. 12 is an illustration of an optical node comprising of a threedegree ROADM on a circuit pack with an externalmultiplexer/de-multiplexer circuit pack.

FIG. 13 is an illustration of an optical node comprising of a threedegree ROADM on a circuit pack utilizing a wavelength equalizing arraycontaining twelve wavelength equalizers, with an externalmultiplexer/de-multiplexer circuit pack.

FIG. 14 is an illustration of an alternative embodiment of an opticalnode comprising of a three degree ROADM on a circuit pack utilizing awavelength equalizing array containing twelve wavelength equalizers,with an external multiplexer/de-multiplexer circuit pack.

FIG. 15 is an illustration of a two degree optical node comprising of atwo degree ROADM on a circuit pack that can be expanded to a four degreeoptical node.

FIG. 16A is an illustration of a four degree optical node comprising oftwo 2-degree ROADM circuit packs, with a single externalmultiplexer/de-multiplexer circuit pack.

FIG. 16B is an illustration of a four degree optical node comprising oftwo 2-degree ROADM circuit packs, with two externalmultiplexer/de-multiplexer circuit packs.

FIG. 17 is an illustration of a two degree optical node utilizing awavelength equalizing array comprising of a two degree ROADM on acircuit pack that can be expanded to a four degree optical node, with anexternal multiplexer/de-multiplexer circuit pack.

FIG. 18 is an illustration of an alternative embodiment of an opticalnode comprising of a two degree ROADM on a circuit pack that can beexpanded to a four degree optical node, with an externalmultiplexer/de-multiplexer circuit pack.

FIG. 19 is an illustration of an optical node comprising of a two degreeROADM on a circuit pack that contains two optical channel monitorsutilizing photo diodes.

FIG. 20 is an illustration of an optical node comprising of a two degreeROADM on a circuit pack with internal transponders, and an externalmultiplexer/de-multiplexer circuit pack. FIG. 21 is an illustration ofan optical node comprising of a three degree

ROADM on a circuit pack with internal transponders, and an externalmultiplexer/de-multiplexer circuit pack.

FIG. 22 is an illustration of a first embodiment of an optical nodecomprising of an expandable two degree ROADM on a circuit pack withinternal transponders, and an external multiplexer/de-multiplexercircuit pack.

FIG. 23 is an illustration of a second embodiment of an optical nodecomprising of an expandable two degree ROADM on a circuit pack withinternal transponders, and an external multiplexer/de-multiplexercircuit pack.

FIG. 24 is an illustration of a third embodiment of an optical nodecomprising of an expandable two degree ROADM on a circuit pack, and anexternal multiplexer/de-multiplexer circuit pack with internaltransponders.

FIG. 25 is an illustration of a ROADM circuit pack comprising of awavelength equalizing array and front panel pluggable amplifiers.

FIG. 26 is an alternative illustration of a ROADM circuit packcomprising of a wavelength equalizing array and front panel pluggableamplifiers.

FIG. 27 is a flow diagram corresponding to a method of constructing amulti-degree optical node utilizing a wavelength equalizing array.

DETAILED DESCRIPTION

A description of example embodiments of the invention follows.

FIG. 1 is an illustration of a wavelength equalizer 100 comprising of; awavelength de-multiplexer (DMUX) 101 that is used to separate acomposite Wavelength Division Multiplexed (WDM) signal arriving at input104 into r number of individual wavelengths, a plurality of ElectricalVariable Optical Attenuators (EVOAs) 103 used to partially or fullyattenuate the individual wavelengths, and a wavelength multiplexer (MUX)102 that is used to combine r number of individual wavelengths into acomposite Wavelength Division Multiplexed (WDM) signal for transmissionat output 105. In addition to its optical elements (MUX, DMUX, andEVOAs), the wavelength equalizer 100 contains electronic circuitry (notshown) used to control the EVOAs, and a user interface (not shown) thatis used to program the electronic circuitry of the EVOAs. The opticalprocessing of each individual wavelength may be independentlycontrolled. The optical power level of each individual wavelength may beattenuated by a programmable amount by sending a command through theuser interface. The command is used by the electronic circuitry to setthe attenuation value of the appropriate EVOA. Additionally, eachindividual EVOA can be program to substantially block the lightassociated with an incoming optical wavelength. Controlled attenuationranges for typical EVOAs are 0 to 15 dB, or 0 to 25 dB. Blockingattenuation is typically 35 dB or 40 dB.

The device 100 is referred to as a wavelength equalizer because theEVOAs 103 can be used to equalize the power levels of all thewavelengths inputted into the device. Therefore, if wavelengths withunequal power levels are applied to input 104, the EVOAs can beconfigured so that the wavelengths exiting at 105 have substantially thesame optical power level with respect to one another. The device 100 isalso often referred to as a wavelength blocker, or as a one-by-onewavelength selective switch.

FIG. 2 is an illustration of a wavelength equalizing array 200 containedwithin a single device. The wavelength equalizing array 200 contains sixwavelength equalizers 201 a-f that may be of the type 100 illustrated inFIG. 1. The wavelength equalizing array 200 contains six optical inputs(IN1-IN6) 202 a-f that are attached to the inputs of the wavelengthequalizers, and six optical outputs (OUT1-OUT6) 203 a-f that areattached to the outputs of the wavelength equalizers. The electroniccircuitry (not shown) used to control the EVOAs 204 may reside withinthe wavelength equalizing array device, or may reside external to thewavelength equalizing array device.

FIG. 3 (300) is an illustration of three different wavelength equalizingarrays 310 350, and 380. Each array may be contained within a singledevice. Wavelength equalizing array 310 contains ten wavelengthequalizers that may be of the type 100 illustrated in FIG. 1. Wavelengthequalizing array 350 contains twelve wavelength equalizers that may beof the type 100 illustrated in FIG. 1. Wavelength equalizing array 380contains u wavelength equalizers that may be of the type 100 illustratedin FIG. 1 (wherein u can be any integer value). Although wavelengthequalizing arrays 200, 310, 350 and 380 illustrate arrays with six, ten,twelve and u wavelength equalizers respectively, in general there is nolimit to the number of wavelength equalizers that can be placed within asingle device. Therefore, arrays with sixteen, twenty-four, orthirty-two wavelength equalizers may be possible.

Multiple different technologies may be used to implement the wavelengthequalizing arrays 200, 310, 350 and 380, including Planer LightwaveCircuit (PLC) technology and various free-space optical technologiessuch as Liquid Crystal on Silicon (LCoS). A single Liquid Crystal onSilicon substrate may be used to implement a wavelength equalizing arraycontaining any number of wavelength equalizers. The WavelengthProcessing Array (WPA-12) from Santec Corporation is an example of acommercially available wavelength equalizing array containing twelvewavelength equalizers. The wavelength equalizing arrays 200, 310, 350and 380 may be implemented by placing PLC based EVOAs and multiplexers(Arrayed Waveguide Gratings (AWG)) on a single substrate.

PLC based technologies and free-space optical technologies also providethe means to augment the wavelength equalizing arrays with additionalcomponents in order to realize additional functionality. An example ofthis is illustrated in FIG. 4. FIG. 4 illustrates a wavelengthequalizing array 400 that contains six wavelength equalizers 100 a-faugmented with some additional optical components comprising of 1×2optical switches, 2×1 optical switches, and variable optical couplers.The additional components provide the ability for two wavelengthequalizers to perform either a 2 by 1 or 1 by 2 wavelength selectiveswitch (WSS) function. A 1 by p wavelength selective switch is definedto be an optical device—with one WDM input port and p WDM outputports—that can be configured to direct individual wavelengths arrivingon its input port to any of its p output ports. Similarly, a p by 1wavelength selective switch is defined to be an optical device—with oneWDM output port and p WDM input ports—that can be configured to directindividual wavelengths arriving on any of its input ports to its singleoutput port.

In FIG. 4 three 2 by 1 WSS functions are implemented 401 a-c. For 2 by 1WSS 401 a, the variable coupler 404 a is used to combine the wavelengthsfrom wavelength equalizers 100 a and 100 b. For this case, 1 by 2optical switches 402 a and 403 a are both configured to forward theirincoming wavelengths to variable coupler 404 a, and variable coupler 404a is configured as a 50/50 optical coupler (i.e., a coupler thatforwards an equal amount of light from each of its two inputs). Ifwavelength number 1 (with frequency 1) is routed from IN1 406 a to OUT1407 a, then wavelength number 1 (with frequency 1) arriving at IN2 406 bmust be blocked by wavelength equalizer 100 b so as not to causecontention with the wavelength number 1 exiting wavelength equalizer 100a. By appropriately blocking and passing wavelengths through 100 a and100 b, up to r number of wavelengths may exit through port OUT1 407 a.

The variable coupler 404 a provides the ability to forward unequalamounts of light from wavelength equalizers 100 a and 100 b to outputport OUT1. This may be a useful feature when, for example, thewavelengths arriving at input port IN1 406 a all have substantiallylower optical power levels than the wavelengths arriving at input portIN2 406 b. For this case, variable attenuator 404 a may be programmed toallow more light from 100 a and less light from 100 b. Alternatively,the variable coupler 404 a may be replaced with a fixed coupler thatforwards an equal amount of light from each of its two inputs.

In FIG. 4, optical switches 402 a, 403 a, and 405 a, provide the abilityfor the two wavelength equalizers 100 a and 100 b to be configured aseither individual 1 by 1 WSS devices or a single 2 by 1 WSS device. Whenswitches 402 a and 403 a are configured to switch their input light tocoupler 404 a, then the two wavelength equalizers 100 a and 100 b areconfigured as a single 2 by 1 WSS. When switches 402 a and 403 a areconfigured to switch their input light away from coupler 404 a, then thetwo wavelength equalizers 100 a and 100 b are configured as individual 1by 1 WSS devices. Switch 405 a is used to switch the output port OUT1407 a between the two functionalities (i.e., either a single 2 by 1 WSSor a single 1 by 1 WSS device).

Note that it's possible to eliminate switches 402 a and 405 a when avariable coupler is used that can substantially direct to its outputport all the light from one of its input ports. For this case, theoutput from 100 a is directly routed to the upper input of variablecoupler 404 a. Then when 401 a is programmed to be two individual 1 by 1WSS devices, variable coupler 404 a is programmed to direct to itsoutput all of the light from 100 a and none of the light from switch 403a.

It can also be noted that each set of dual wavelength equalizers 401 a-ccan be used as 1 by 2 WSS devices by inputting signals to port OUT1 407a while outputting signals to ports IN1 406 a and IN2 406 b (i.e.,operating the 2 by 1 WSS in the reverse direction).

It can also be noted that each set of dual wavelength equalizers 401 a-ccan be independently programmed to be either a single 2 by 1 WSS deviceor two individual 1 by 1 WSS devices. As an example, 401 a may beprogrammed to be a 2 by 1 WSS device, while 401 b and 401 c may beprogrammed to be 1 by 1 WSS devices.

Although wavelength equalizing array 400 is shown as implemented withindividual switches, multiplexers, and de-multiplexers, withoutdeparting from the spirit of the invention, the actual filtering andswitching functions can be accomplished with other means, includingusing free-space optics wherein multiple switching and filteringfunctions are combined in order to accomplish the identical switchingand filtering functionality.

FIG. 5 (500) illustrates an alternative method of implementing asix-input wavelength equalizing array 510 that can function asindividual 1 by 1 WSS devices or 2 by 1 WSS devices. The advantage ofimplementation 510 over implementation 400 is that the 2 by 1 WSSinstances 511 a-c in 510 have lower insertion losses than the 2 by 1 WSSinstances 401 a-c in 400. This is because implementation 510 eliminatesthe large insertion loss of the variable coupler 404 a. However, inorder to eliminate the coupler, additional complexity is added in theform of 2r number of optical switch functions (1×2 and 2×1) 513, 514.

In the 510 implementation, individual 1 by 1 WSS functions are obtainedby programming the optical switches 513 such that all wavelengthsentering a given input INx are forwarded to the corresponding outputOUTx. For instance, all the wavelengths entering input 515 a areforwarded to output 516 a, and not to output 516 b. When using a set ofdual wavelength equalizers to form a 2 by 1 WSS function (511 a, forexample), the optical switches 513 are programmed such that allwavelengths entering IN1 515 a are forwarded to switches 514, and thenswitches 514 are used to route individual wavelengths to OUT2 516 b fromeither wavelengths entering on port IN1 515 a or port IN2 515 b.

An alternative structure for the dual wavelength equalizers is 511 d. Inthis structure r number of individual 1×2 switches are replaced with asingle 1×2 switch 520 at the expense of an extra DMUX.

The set of dual wavelength equalizers 511 a-c can operate as either 2 by1 WSS devices or 1 by 2 WSS devices. For example, when operatinginstance 511 a as a 2 by 1 device, input ports IN1 515 a and IN2 515 band output port OUT2 516 b are used. Alternatively, when operatinginstance 511 a as a 1 by 2 device, ports OUT1 516 a, OUT2 516 b and inIN1 515 a are used.

The dual wavelength equalizer 511 d can operate as a 1 by 2 WSS deviceby running the device backwards using OUT2 522 b as the input (not 522a).

FIG. 6 shows a wavelength equalizing array 600 that is constructedidentically to the wavelength equalizing array 510, except that array600 contains ten wavelength equalizers instead of only six.

FIG. 7 shows a wavelength equalizing array 700 containing six wavelengthequalizers 701 a-f that can be configured (by setting the 1×2, and 2×1switches appropriately) as either 1 by 3 WSS devices, 1 by 2 WSS devicesor 1 by 1 WSS devices. A first 1 by 3 device is formed by the top threewavelength equalizers 701 a-c (using IN1 702 a, OUT1 703 a, OUT2 703 b,and OUT3 703 c), while a second 1 by 3 device is formed by the bottomthree wavelength equalizers 701 d-f (using IN4 702 d, OUT4 703 d, OUT5703 e, and OUT6 703 f). In order to use the wavelength equalizing arrayas 3 by 1 WSS devices, the wavelength equalizing array is used in thereverse direction, using all output ports as inputs, and using the IN1port 702 a as the output port for the top 3 by 1, and using the IN4 port702 d as the output port for the bottom 3 by 1.

The wavelength equalizing array 700 can alternatively be used to createthree 1 by 2 WSS devices by using IN1 702 a, OUT1 703 a and OUT2 703 bas the first 1 by 2 WSS, using IN3 702 c, OUT3 703 c, and OUT4 703 d asthe second 1 by 2 WSS, and using INS 702 e, OUTS 703 e, and OUT6 703 fas the third 1 by 2 WSS. Similarly, the wavelength equalizing array 700can be used to create three 2 by 1 WSS devices by using IN1 702 a, IN2702 b, and OUT2 703 b as the first 2 by 1 WSS, using IN3 702 c, IN4 702d, and OUT4 703 d as the second 2 by 1 WSS, and using IN5 702 e, IN6 702f, and OUT6 703 f as the third 2 by 1 WSS.

Finally the wavelength equalizing array 700 can be used to create six 1by 1 WSS devices by programming all switches such that all inputwavelengths arriving on a given port INx are forwarded to thecorresponding output port OUTx.

Any combination of 1 by 3 WSS devices, 1 by 2 WSS devices, and 1 by 1WSS devices can be created using the wavelength equalizing array 700.For instance, wavelength equalizing array 700 can be used to implement asingle 1 by 3 WSS device, a single 1 by 2 WSS device, and a single 1 by1 WSS device. Alternatively, the wavelength equalizing array 700 can beused to implement two 1 by 2 WSS devices, and two 1 by 1 WSS devices. Inthis way, a single wavelength equalizing array device can be used in aproduct to create a product with multiple distinct capabilities, whilenot incurring the cost and complexity of creating a single 6 by 6 WSSdevice.

Although wavelength equalizing array 700 is shown as implemented withindividual switches, multiplexers, and de-multiplexers, the actualswitching functions can be accomplished with free-space optics whereinmultiple switching and filtering functions are combined in order toaccomplish identical switching and filtering functionality.

In general, for a wavelength equalizing array that can be configured aseither 1 by 1 WSS devices or 2 by 1 WSS devices, if the device can beused to construct a maximum of n 1 by 1 WSS devices, then the maximumnumber of 2 by 1 WSS devices that the array can be used to create is n/2devices, since each 2 by 1 device requires the resources associated withtwo 1 by 1 WSS devices.

For a wavelength equalizing array with a maximum of n number of 1 by 1WSS devices that can be configured as either 1 by 1 WSS devices or 2 by1 WSS devices, if the device is configured to have m number of 1 by 1WSS devices, then the maximum number of 2 by 1 devices that can also beconfigured is equal to (n−m)/2.

For a wavelength equalizing array that can be configured as either 1 by1 WSS devices or 3 by 1 WSS devices, if the device can be used toconstruct a maximum of n 1 by 1 WSS devices, then the maximum number of3 by 1 WSS devices that the array can be used to create is n/3 devices,since each 3 by 1 device requires the resources associated with three 1by 1 WSS devices.

For a wavelength equalizing array with a maximum of n number of 1 by 1WSS devices that can be configured as either 1 by 1 WSS devices or 3 by1 WSS devices, if the device is configured to have m number of 1 by 1WSS devices, then the maximum number of 3 by 1 devices that can also beconfigured is equal to (n−m)/3.

In general, a wavelength equalizing array can be partitioned into anarray of k₁1×1, k₂1×2, k₃1×3 . . . , k_(p)1×p wavelength selectiveswitches, where p is any integer number greater than 1, and k_(j) is anyinteger value greater than or equal to 0. For this case, if n is themaximum number of 1×1 wavelength selective switches in the at least onewavelength equalizing array, then Σ_(i=1) ^(p)i×k_(i)≦n.

FIG. 8 depicts a wavelength equalizing array 800 containing twoinstances (700 a, 700 b) of wavelength equalizing array 700. In FIG. 8,the wavelength equalizing array 800 can be partitioned into four 1 by 3WSS devices 810 a-d.

FIG. 9 shows an optical node 900 comprising of a two-degreeReconfigurable Optical Add/Drop Multiplexer (ROADM) 910 on a circuitpack with an external multiplexer/de-multiplexer circuit pack 920. Eachline interface on the ROADM (Line In/Out West 901 a-b, and Line In/OUTEast 902 a-b) represents an optical degree. In addition, optical node900 contains a port common to both optical degrees (common port 970 a-b)that is connectable to a plurality of directionless add/drop ports 961and 960. Six wavelength equalizers 905 a-f are used in the design—threefor each degree. Wavelength equalizer WE1 905 a is used to either passor block wavelengths from the West Line interface 901 a to themultiplexer/de-multiplexer circuit pack 920 attached to the common port970 a-b. Similarly, wavelength equalizer WE4 905 d is used to eitherpass or block wavelengths from the East Line interface 902 a to themultiplexer/de-multiplexer circuit pack 920 attached to the common port970 a-b. The wavelengths from WE1 905 a and WE4 905 d are combinedtogether using optical coupler 934, and then they are forwarded to themultiplexer/de-multiplexer circuit pack 920 via optional opticalamplifier 942 through the common optical port 970 a.

Wavelength equalizer WE3 905 c is used to either pass or blockwavelengths from the common port 970 b to the West Line interface 901 b.It is also used to equalize the power levels of the wavelengths exitingout the West Line interface 901 b from the multiplexer/de-multiplexercircuit pack 920. Similarly, wavelength equalizer WE6 905 f is used toeither pass or block wavelengths from the common port 970 b to the EastLine interface 902 b. It is also used to equalize the power levels ofthe wavelengths exiting out the East Line interface 902 b from themultiplexer/de-multiplexer circuit pack 920.

Wavelength equalizer WE2 905 b is used to either pass or blockwavelengths from the East Line interface 902 a to the West Lineinterface 901 b. It is also used to equalize the power levels of thewavelengths exiting out the West Line interface 901 b from the East Lineinterface 902 a. Similarly, wavelength equalizer WE5 905 e is used toeither pass or block wavelengths from the West Line interface 901 a tothe East Line interface 902 b. It is also used to equalize the powerlevels of the wavelengths exiting out the East Line interface 902 b fromthe West Line interface 901 a.

Optional input optical amplifiers 940 a-b are used to optically amplifywavelengths arriving from the West 901 a and East 902 a Line interfaces.These amplifiers can be constructed using Erbium Doped Fiber Amplifier(EDFA) technology or some other suitable technology.

Optical coupler 930 is used to broadcast all the wavelengths from theWest Line interface 901 a to both wavelength equalizer WE1 905 a and WE5905 e. Similarly, optical coupler 932 is used to broadcast all thewavelengths from the East Line interface 902 a to both wavelengthequalizer WE2 905 b and WE4 905 d.

Optical coupler 931 is used to combine the wavelengths from wavelengthequalizers WE2 905 b and WE3 905 c into one composite WDM signal that isoptically amplified with output optical amplifier 941 a. Similarly,optical coupler 933 is used to combine the wavelengths from wavelengthequalizers WE5 905 e and WE6 905 f into one composite WDM signal that isoptically amplified with output optical amplifier 941 b.

Optional optical amplifier 943 receives added wavelengths from themultiplexer/de-multiplexer circuit pack 920 via port 970 b, andoptically amplifies the wavelengths before forwarding the amplifiedwavelengths to optical coupler 935. Optical coupler 935 is used tobroadcast the added wavelengths to both the West Line interface 901 band East Line interface 902 b via WE3 905 c and WE6 905 f respectively.

Located on the multiplexer/de-multiplexer circuit pack 920 is aplurality (r) of add/drop ports 961, 960. Individual wavelengths areadded to the multiplexer/de-multiplexer circuit pack and thenmultiplexed via multiplexer 951 into a composite WDM signal that is thenforwarded to the ROADM circuit pack 910. In the drop direction on 920, acomposite WDM signal is received from the common port 970 a of the ROADMcircuit pack 910 and then it is de-multiplexed into individualwavelengths using de-multiplexer 950. Each de-multiplexed wavelength isthen forwarded to a specific drop port 960 of the de-multiplexer. Themultiplexer and de-multiplexer may be implemented using ArrayedWaveguide Grating (AWG) technology, or some other suitable technology.Devices that process individual wavelengths for transmission—such asoptical transponders—can be used to supply and receive wavelengths toand from the add/drop ports. The common port 970 a-b of the ROADMcircuit pack 910 is connected to the multiplexer/de-multiplexer circuitpack 920 using two optical jumper interconnections 972 a-b.

As can be seen in 900, a single multiplexer/de-multiplexer circuit packis used to add and drop wavelengths to/from both the East and West Lineinterfaces. Therefore, a transponder that is attached to an add/dropport of the multiplexer/de-multiplexer circuit pack 920, can forward andreceive wavelengths to and from any of the two degrees of the ROADMcircuit pack. Because of this, the add/drop ports are referred to asdirectionless add/drop ports—meaning the add drop ports are notdedicated to a particular direction of the optical node. The wavelengthequalizers on the ROADM circuit pack are used to steer the added anddropped wavelengths to and from each degree by appropriately blocking orpassing wavelengths. Therefore, the wavelength equalizers WE1 905 a, WE3905 c, WE4 905 d, and WE6 905 f are said to perform directionlesssteering for the add/drop ports for each degree.

Additionally, the wavelength equalizers on the ROADM circuit pack areused to select which wavelengths from the Line input interfaces areallowed to exit a given output interface (degree), by appropriatelyblocking or passing wavelengths.

Both the ROADM circuit pack 910 and the multiplexer/de-multiplexercircuit pack 920 may contain electrical connectors that allow the twocircuit packs to be plugged into an electrical back plane of anelectrical shelf (not shown). The multiplexer/de-multiplexer circuit 920pack may contain active components (i.e., components requiringelectrical power in order to operate), or it may contain only passivecomponents (athermal AWGs, for example). If themultiplexer/de-multiplexer circuit pack 920 contains only passivecomponents, then the multiplexer/de-multiplexer circuit pack couldoptionally be placed outside of the electrical shelf.

FIG. 10 shows a two degree optical node 1000 that is identical to theoptical node 900, except that a single wavelength equalizing array 200is used to supply all the required wavelength equalizers needed toconstruct the optical node. (Alternatively, multiple smaller wavelengthequalizing arrays could be utilized.) The wavelength equalizers WE1-WE6in 1000 correspond to the wavelength equalizers WE1-WE6 in 900. Morespecifically WE1 1005 a in ROADM circuit pack 1010 corresponds WE1 905 ain ROADM circuit pack 910, WE2 1005 b in 1010 corresponds WE2 905 b in910, WE3 1005 c in 1010 corresponds WE3 905 c in 910, WE4 1005 d in 1010corresponds WE4 905 d in 910, WE5 1005 e in 1010 corresponds WE5 905 ein 910, and WE6 1005 f in 1010 corresponds WE6 905 f in 910. Likewisethe optical couplers 1030, 1031, 1032, 1033, 1034, and 1035 perform thesame functions as their respective counterparts 930, 931, 932, 933, 934,and 935 within ROADM circuit pack 1010. The single wavelength equalizingarray 200 may be identical to the wavelength equalizing array 200discussed in reference to FIG. 2.

A single ROADM circuit pack 1010 supplies all the required opticalcircuitry to construct an optical node with two optical degrees,including input and output amplifiers for each degree, a common port1070 a-b connectable to a plurality of directionless add/drop ports,optical supervisory channel circuitry (not shown), optical channelmonitoring (not shown), and a single wavelength equalizing array 200that is used to both select wavelengths for each optical degree (usingWE2 1005 b and WE3 1005 c for the West degree 1001 b, and using WE5 1005e and WE6 1005 f for the East degree 1002 b) and to performdirectionless steering for the plurality of directionless add/drop ports(using WE1 1005 a and WE4 1005 d in the drop direction, and using WE31005 c and WE6 1005 f in the add direction).

As can be seen in 1000, a single multiplexer/de-multiplexer circuit pack1020 is used to add and drop wavelengths to/from both the East 1002 a-band West 1001 a-b Line interfaces. Therefore, a transponder (not shown)that is attached to an add/drop port of the multiplexer/de-multiplexercircuit pack 1020, can forward and receive wavelengths to/from any ofthe two degrees of the ROADM circuit pack. Because of this, the add/dropports are referred to as directionless add/drop ports—meaning the adddrop ports are not dedicated to a particular direction of the opticalnode. The wavelength equalizers on the ROADM circuit pack are used tosteer the added and dropped wavelengths to and from each degree byappropriately blocking or passing wavelengths. Therefore, the wavelengthequalizers are said to perform directionless steering for the add/dropports.

Additionally, the wavelength equalizers on the ROADM circuit pack 1010are used to select which wavelengths from the Line input interfaces areallowed to exit a given output interface (degree), by appropriatelyblocking or passing wavelengths.

The wavelength equalizing array saves physical space and electricalpower by utilizing common optics and electronics for all the wavelengthequalizers in the array, thus making it more suitable for low-costcompact edge-of-network applications. The single wavelength equalizingarray also provides a means to simplify the construction of the ROADMcircuit pack that it is placed upon.

A preferred embodiment utilizes a “single” wavelength equalizing arrayto construct an optical node. Other embodiments may include using morethan one wavelength equalizing array.

A preferred embodiment is to construct an optical node of at least twooptical degrees using both a first circuit pack and a second circuitpack, wherein the optical node contains at least one wavelengthequalizing array and a plurality of directionless add/drop ports, andwherein the at least one wavelength equalizing array is contained on thefirst circuit pack, and wherein the plurality of direction less add/dropports are contained on the second circuit pack.

Another embodiment comprises of an optical node of at least two opticaldegrees, implemented using a single circuit pack, wherein the opticalnode contains at least one wavelength equalizing array and a pluralityof directionless add/drop ports, and wherein the at least one wavelengthequalizing array and the plurality of directionless add/drop ports arecontained on the single circuit pack.

Another preferred embodiment includes a ROADM circuit pack, comprisingof at least two optical degrees, and a common port connectable to aplurality of directionless add/drop ports, wherein wavelengths from thecommon port may be directed to any of the at least two optical degrees.Additionally, wavelengths from the at least two optical degrees may bedirected to the common port of the ROADM circuit pack. The embodimentmay further include input optical amplification and output opticalamplification for each optical degree. The ROADM circuit pack mayfurther comprise of at least one wavelength equalizing array, whereinthe at least one wavelength equalizing array provides a means to bothselect wavelengths for each degree, and to perform directionlesssteering of wavelengths to and from the plurality of directionlessadd/drop ports, as illustrated in reference to the ROADM shown in FIG.10. In a preferred embodiment, a single wavelength equalizing array isused to construct the ROADM circuit pack. The at least one wavelengthequalizing array may be constructed using a single Liquid Crystal onSilicon substrate, or it may be constructed using planar lightwavecircuitry.

FIG. 11 shows a two degree optical node 1100 that is identical to theoptical node 900, except that a single wavelength equalizing array 510is used to supply all the required wavelength equalizers needed toconstruct the optical node. The wavelength equalizing array 510 may beidentical to the wavelength equalizing array that was described inreference to FIG. 5.

This wavelength equalizing array 510 can be configured to perform thefunction of multiple 2 by 1 WSS devices. Therefore, the function of theoptical couplers 931, 933, and 934 of optical node 900 are additionallyabsorbed within the wavelength equalizing array 510. The 2 by 1 WSSfunction 1140 a performs the function of WE1 905 a, WE4 905 d, andoptical coupler 934 within optical node 900, while the 2 by 1 WSSfunction 1140 b performs the function of WE2 905 b, WE3 905 c, andoptical coupler 931 within optical node 900, and the 2 by 1 WSS function1140 c performs the function of WE5 905 e, WE6 905 f, and opticalcoupler 933 within optical node 900. Optical couplers 1130, 1132, and1135 perform the same functions as their respective counterparts 930,932, and 935 within ROADM circuit pack 910. As can be seen from FIG. 11,using the wavelength equalizing array 510 in place of wavelengthequalizing array 200 further simplifies the ROADM circuit pack due tothe additional level of integration.

FIG. 12 shows an optical node 1200 comprising of a three-degreeReconfigurable Optical Add/Drop Multiplexer (ROADM) 1210 on a circuitpack with an external multiplexer/de-multiplexer circuit pack 1220. Eachline interface on the ROADM (Line In/Out West 1201 a-b, Line In/OUT East1202 a-b, and Line In/OUT South 1203 a-b) represents an optical degree.Twelve wavelength equalizers are used in the design—four for eachdegree. Wavelength equalizer WE1 1205 a is used to either pass or blockwavelengths from the West Line interface 1201 a to themultiplexer/de-multiplexer circuit pack 1220. Similarly, wavelengthequalizer WE5 1205 e and WE9 1205 i are used to either pass or blockwavelengths from the East 1202 a and South 1203 a Line interfaces to themultiplexer/de-multiplexer circuit pack 1220. The wavelengths from WE11205 a, WE5 1205 e, and WE9 1205 i are combined together using opticalcoupler 1234, and then they are forwarded to themultiplexer/de-multiplexer circuit pack 1220 via optional opticalamplifier 1242 through the common port 1270 a.

Wavelength equalizer WE4 1205 d is used to either pass or blockwavelengths from the multiplexer/de-multiplexer circuit pack 1220 to theWest Line interface 1201 b. It is also used to equalize the power levelsof the wavelengths exiting out the West Line interface 1201 b rom themultiplexer/de-multiplexer circuit pack 1220. Similarly, wavelengthequalizers WE8 1205 h and WE12 1205 m are used to either pass or blockwavelengths from the multiplexer/de-multiplexer circuit pack 1220 to theEast 1202 b and South 1203 b Line interfaces. They are also used toequalize the power levels of the wavelengths exiting out the East 1202 band South 1203 b Line interfaces from the multiplexer/de-multiplexercircuit pack 1220.

Wavelength equalizer WE2 1205 b and WE3 1205 c are used to either passor block wavelengths from the East 1202 a and South 1203 a Lineinterfaces to the West Line interface 1201 b. They are also used toequalize the power levels of the wavelengths exiting out the West Lineinterface 1201 b from the East 1202 a and South 1203 a Line interfaces.Similarly, wavelength equalizers WE6 1205 f and WE7 1205 g are used toeither pass or block wavelengths from the West 1201 a and South 1203 aLine interfaces to the East Line interface 1202 b. They are also used toequalize the power levels of the wavelengths exiting out the East Lineinterface 1202 b from the West 1201 a and South 1203 a Line interfaces.Lastly, wavelength equalizers WE10 1205 j and WE11 1205 k are used toeither pass or block wavelengths from the West 1201 a and East 1202 aLine interfaces to the South Line interface 1203 b. They are also usedto equalize the power levels of the wavelengths exiting out the SouthLine interface 1203 b from the West 1201 a and East 1202 a Lineinterfaces.

Optional input optical amplifiers 1240 a-c are used to optically amplifywavelengths arriving from the West 1201 a, East 1202 a, and South 1203 aLine interfaces.

Optical coupler 1230 is used to broadcast all the wavelengths from theWest Line interface 1201 a to wavelength equalizers WE1 1205 a, WE6 1205f , and WE10 1205 j. Similarly, optical coupler 1232 is used tobroadcast all the wavelengths from the East Line interface 1202 a towavelength equalizer s WE2 1205 b, WE5 1205 e, and WE11 1205 k. Lastly,optical coupler 1236 is used to broadcast all the wavelengths from theSouth Line interface 1203 a to wavelength equalizers WE3 1205 c, WE71205 g, and WE9 1205 i.

Optical coupler 1231 is used to combine the wavelengths from wavelengthequalizers WE2 1205 b, WE3 1205 c and WE4 1205 d into one composite WDMsignal that is optically amplified with output optical amplifier 1241 a.Similarly, optical coupler 1233 is used to combine the wavelengths fromwavelength equalizers WE6 1205 f, WE7 1205 g, and WE8 1205 h into onecomposite WDM signal that is optically amplified with output opticalamplifier 1241 b. Lastly, optical coupler 1237 is used to combine thewavelengths from wavelength equalizers WE10 1205 j, WE11 1205 k, andWE12 1205 m into one composite WDM signal that is optically amplifiedwith output optical amplifier 1241 c.

Optional optical amplifier 1243 receives added wavelengths from themultiplexer/de-multiplexer circuit pack 1220 via common port 1270 b, andoptically amplifies the wavelengths before forwarding the amplifiedwavelengths to optical coupler 1235. Optical coupler 1235 is used tobroadcast the added wavelengths to the West Line interface 1201 b, theEast Line interface 1202 b, and the South Line Interface 1203 b via WE41205 d, WE8 1205 h, and WE12 1205 m respectively.

Located on the multiplexer/de-multiplexer circuit pack 1220 is aplurality (r) of add/drop ports 1260, 1261. Individual wavelengths areadded to the multiplexer/de-multiplexer circuit pack and thenmultiplexed via multiplexer 1251 into a composite WDM signal that isthen forwarded to the ROADM circuit pack 1210 via the common port 1270 bof the ROADM circuit pack. In the drop direction on 1220, a compositeWDM signal is received from the ROADM circuit pack 1210 via the commonport 1270 a and then it is de-multiplexed into individual wavelengthsusing de-multiplexer 1250. Each de-multiplexed wavelength is thenforwarded to a specific drop port of the de-multiplexer. The multiplexerand de-multiplexer may be implemented using Arrayed Waveguide Grating(AWG) technology, or some other suitable technology. Devices thatprocess individual wavelengths for transmission—such as opticaltransponders (not shown)—can be used to supply and receive wavelengthsfrom the add/drop ports.

As can be seen in 1200, a single multiplexer/de-multiplexer circuit pack1220 is used to add and drop wavelengths to/from the East, West, andSouth Line interfaces. Therefore, a transponder that is attached to anadd/drop port of the multiplexer/de-multiplexer circuit pack 1220, canforward and receive wavelengths from any of the three degrees of theROADM circuit pack. Because of this, the add/drop ports are referred toas directionless add/drop ports—meaning the add/drop ports are notdedicated to a particular direction of the optical node. The wavelengthequalizers on the ROADM circuit pack are used to steer the added anddropped wavelengths to and from each degree by appropriately blocking orpassing wavelengths. Therefore, the wavelength equalizers are said toperform directionless steering for the add/drop ports.

Additionally, the wavelength equalizers on the ROADM circuit pack areused to select which wavelengths from the Line input interfaces areallowed to exit a given output interface (degree), by appropriatelyblocking or passing wavelengths.

FIG. 13 shows a three degree optical node 1300 that is identical to theoptical node 1200, except that a single wavelength equalizing array 350is used to supply all the required wavelength equalizers needed toconstruct the optical node. (Alternatively, multiple smaller wavelengthequalizing arrays could be utilized.) The wavelength equalizers WE1-WE121305 a-m in 1300 correspond to the wavelength equalizers WE1-WE12 1205a-m in 1200. The single wavelength equalizing array 350 may be identicalto the wavelength equalizing array 350 discussed in reference to FIG. 3.

A single ROADM circuit pack 1310 supplies all the required opticalcircuitry to support three optical degrees, including input and outputamplifiers for each degree, a common optical port connectable to aplurality of directionless add/drop ports, optical supervisory channelcircuitry (not shown), optical channel monitoring (not shown), and asingle wavelength equalizing array 350 that is used to both selectwavelengths for each degree and to perform directionless steering forthe add/drop ports of each degree.

As can be seen in 1300, a single multiplexer/de-multiplexer circuit pack1320 is used to add and drop wavelengths to/from the East 1302 a-b, West1301 a-b, and South 1303 a-b Line interfaces. Therefore, a transponderthat is attached to an add/drop port of the multiplexer/de-multiplexercircuit pack 1320, can forward and receive wavelengths to/from any ofthe three degrees of the ROADM circuit pack. Because of this, theadd/drop ports are referred to as directionless add/drop ports—meaningthe add drop ports are not dedicated to a particular direction of theoptical node. The wavelength equalizers on the ROADM circuit pack areused to steer the added and dropped wavelengths to and from each degreeby appropriately blocking or passing wavelengths. Therefore, thewavelength equalizers are said to perform directionless steering for theadd/drop ports.

Additionally, the wavelength equalizers on the ROADM circuit pack 1310are used to select which wavelengths from the Line input interfaces areallowed to exit a given output Line interface (degree), by appropriatelyblocking or passing wavelengths.

The ROADM circuit pack 1310 is constructed on one or more printedcircuit boards that are bound together electrically and mechanically sothat the circuit pack can be plugged into a backplane as a singleentity. The ROADM circuit pack additionally contains a front panel (usedto house the optical connectors associated with the optical ports on theROADM), electrical control circuitry (used to take in user commandsneeded to control the ROADM), power supply circuitry (used to providethe various voltage levels and electrical currents needed to power thevarious components on the ROADM), and one or more backplane connectors(needed to connect electrical signals on the ROADM circuit pack tosignals on the back plane that the ROADM card is plugged into).

Alternatively, the optical multiplexer/de-multiplexer circuitry on themultiplexer/de-multiplexer circuit pack 1320 could be placed on theROADM circuit pack 1310, thus eliminating a circuit pack in the opticalnode.

The add/drop ports on the multiplexer/de-multiplexer circuit pack 1320are considered to be colored add/drop ports. This is because eachadd/drop port is used to support a particular optical frequency(wavelength). So therefore, add/drop port 1 will only support wavelengthfrequency 1, and therefore a transponder attached to add/drop port 1must only generate wavelength frequency 1. An alternative (not shown) isto supply an alternative multiplexer/de-multiplexer circuit pack thatcontains colorless add/drop ports. A colorless add/drop port can be usedto support any of the r wavelength frequencies associated with the ROADMcircuit pack, and therefore a transponder attached to add/drop port 1 isallowed to generate any of the r wavelength frequencies.

The wavelength equalizing array (350) saves physical space andelectrical power by utilizing common optics and electronics for all thewavelength equalizers in the array, thus making it more suitable forcompact edge-of-network applications. The single wavelength equalizingarray also provides a means to simplify the construction of the ROADMcircuit pack that it is placed upon. Furthermore, the wavelengthequalizing array 350 provides the flexibility to generate alternativefunctions and architectures by simply changing the manner in which thewavelength equalizing array is connected to other optical components onthe ROADM circuit pack.

In summary, optical node 1300 comprises of three degrees withcorresponding optical interfaces 1301 a-b, 1302 a-b, and 1303 a-b, aplurality of directionless add/drop ports 1361, 1360, and at least onewavelength equalizing array 350, wherein the at least one wavelengthequalizing array 350 is used to both select wavelengths for each opticaldegree (via wavelength equalizers 1305 b-d, 1305 f-h, & 1305 j-m), andto perform directionless steering for the plurality of directionlessadd/drop ports 1361,1360 (via wavelength equalizers 1305 a, 1305 d, 1305e, 1305 h, 1305 i, 1305 m). The three degree optical node may beimplemented with a single ROADM circuit pack comprising of all threedegrees.

FIG. 14 shows a three degree optical node 1400 that is identical to theoptical node 1200, except that a single wavelength equalizing array 800is used to supply all the required wavelength equalizers needed toconstruct the optical node. The wavelength equalizing array that is usedis the wavelength equalizing array 800 that was described in referenceto FIG. 8. This wavelength equalizing array can be configured to performthe function of multiple 1 by 3 WSS devices. Therefore, the function ofthe optical couplers 1230, 1232, 1235, and 1236 of optical node 1200 areadditionally absorbed within the wavelength equalizing array 800. The 3by 1 WSS function 1440 a performs the function of WE1 1205 a, WE6 1205f, WE10 1205 j, and optical coupler 1230 within optical node 1200, whilethe 3 by 1 WSS function 1440 b performs the function of WE3 1205 c, WE71205 g, WE9 1205 i, and optical coupler 1236 within optical node 1200,and the 3 by 1 WSS function 1440 c performs the function of WE2 1205 b,WE5 1205 e, WE11 1205 k, and optical coupler 1232 within optical node1200, and the 3 by 1 WSS function 1440 d performs the function of WE41205 d, WE8 1205 h, WE12 1205 m, and optical coupler 1235 within opticalnode 1200 . Couplers 1431, 1433, 1434, and 1437, correspond to thecouplers 1231, 1233, 1234, and 1237 within ROADM circuit pack 1210. Ascan be seen from FIG. 14, using the wavelength equalizing array 800 inplace of wavelength equalizing array 310 further simplifies the ROADMcircuit pack due to the additional level of integration.

FIG. 15 shows an optical node 1500 comprising of a two-degreeReconfigurable Optical Add/Drop Multiplexer (ROADM) 1510 on a circuitpack with an external multiplexer/de-multiplexer circuit pack 1520. TheROADM circuit pack can be used as a stand-alone ROADM in a two degreenode, or it can be paired with a second identical ROADM circuit pack inorder to form a four degree node. The four Express ports (Express Out 1& 2 and Express In 1 & 2 1560 a-d) are used to interconnect the twoROADMs when two ROADM circuit packs are paired to form a four degreenode. Each line interface on the ROADM (Line In/Out 1 1501 a-b and LineIn/Out 2 1502 a-b) represents an optical degree. Ten wavelengthequalizers 1505 a-j are used in the embodiment—five for each degree.Wavelength equalizer WE1 1505 a is used to either pass or blockwavelengths from the Line 1 interface 1501 a to themultiplexer/de-multiplexer circuit pack 1520. Similarly, wavelengthequalizer WE6 1505 f is used to either pass or block wavelengths fromthe Line 2 interface 1502 a to the multiplexer/de-multiplexer circuitpack 1520. The wavelengths from WE1 1505 a and WE6 1505 f are combinedtogether using optical coupler 1534, and then they are forwarded to themultiplexer/de-multiplexer circuit pack 1520 via optional opticalamplifier 1542 through common optical port 1570 a.

Wavelength equalizer WE5 1505 e is used to either pass or blockwavelengths from the multiplexer/de-multiplexer circuit pack 1520 to theLine 1 interface 1501 b. It is also used to equalize the power levels ofthe wavelengths exiting out the Line 1 interface 1501 b from themultiplexer/de-multiplexer circuit pack 1520. Similarly, wavelengthequalizer WE10 1505 j is used to either pass or block wavelengths fromthe multiplexer/de-multiplexer circuit pack 1520 to Line 2 interface1502 b. WE10 1505 j is also used to equalize the power levels of thewavelengths exiting out the Line 2 interface 1502 b from themultiplexer/de-multiplexer circuit pack 1520.

Wavelength equalizer WE2 1505 b, WE3 1505 c, and WE4 1505 d are used toeither pass or block wavelengths from the Express 1560 b-c and Line 21502 a interfaces to the Line 1 interface 1501 b. They are also used toequalize the power levels of the wavelengths exiting out the Line 1interface 1501 b from the Express 1560 b-c and Line 2 1502 a interfaces.Similarly, wavelength equalizers WE7 1505 g, WE8 1505 h, and WE9 1505 iare used to either pass or block wavelengths from the Line 1 1501 a andExpress 1560 b-c interfaces to the Line 2 interface 1502 b. They arealso used to equalize the power levels of the wavelengths exiting outthe Line 2 1502 b interface from the Line 1 1501 a and Express 1560 b-cinterfaces.

Optical couplers 1580 a and 1580 b are used to broadcast the Express In1 1560 b and Express In 2 1560 c optical input signals to both the Line1 1501 b and Line 2 1502 b interface directions.

Optional input optical amplifiers 1540 a-b are used to optically amplifywavelengths arriving from the Line 1 1501 a and 2 Line 2 1502 ainterfaces.

Optical coupler 1530 is used to broadcast all the wavelengths from theLine 1 interface 1501 a to wavelength equalizers WE1 15050 a and WE71505 g, and the Express Out 1 port 1560 a. Similarly, optical coupler1532 is used to broadcast all the wavelengths from the Line 2 interface1502 a to wavelength equalizers WE2 1505 b and WE6 1505 f, and theExpress Out 2 port 1560 d.

Optical coupler 1531 is used to combine the wavelengths from wavelengthequalizers WE2 1505 b through WE5 1505 e into one composite WDM signalthat is optically amplified with output optical amplifier 1541 a.Similarly, optical coupler 1533 is used to combine the wavelengths fromwavelength equalizers WE7 1505 g through WE10 1505 j into one compositeWDM signal that is optically amplified with output optical amplifier1541 b.

Optional optical amplifier 1543 receives added wavelengths from themultiplexer/de-multiplexer circuit pack 1520 via common port 1570 b, andoptically amplifies the wavelengths before forwarding the amplifiedwavelengths to optical coupler 1535. Optical coupler 1535 is used tobroadcast the added wavelengths to the Line 1 interface 1501 b, and theLine 2 interface 1502 b via WE5 1505 e and WE10 1505 j respectively.

Located on the multiplexer/de-multiplexer circuit pack 1520 is aplurality (r) of add/drop ports 1561, 1560. Individual wavelengths areadded to the multiplexer/de-multiplexer circuit pack and thenmultiplexed via multiplexer 1551 into a composite WDM signal that isthen forwarded to the ROADM circuit pack 1510 via common port 1570 b. Inthe drop direction on 1520, a composite WDM signal is received fromcommon port 1570 a of the ROADM circuit pack and then it isde-multiplexed into individual wavelengths using de-multiplexer 1550.Each de-multiplexed wavelength is then forwarded to a specific drop portof the de-multiplexer. The multiplexer and de-multiplexer may beimplemented using Arrayed Waveguide Grating (AWG) technology, or someother suitable technology. Devices that process individual wavelengthsfor transmission—such as optical transponders—can be used to supply andreceive wavelengths from the add/drop ports.

It should be noted that multiplexer/de-multiplexer circuit pack 1520contains two WDM input ports (IN1 1575 b and IN2 1575 a), and two WDMoutput ports (OUT1 1575 d and OUT2 1575 c). This is to allow connectionto up to two ROADM circuit packs 1510, as illustrated in FIG. 16A. Anoptical coupler 1555 is used combine composite WDM signals from twoROADM circuit packs 1510 before forwarding the composite WDM signal tode-multiplexer 1550. An optical coupler 1556 is used to broadcast thecomposite WDM signal from multiplexer 1551 to two ROADM circuit packs1510.

As can be seen in 1500, a single multiplexer/de-multiplexer circuit pack1520 is used to add and drop wavelengths to/from the Line 1 1501 a andLine 2 1502 a interfaces. Therefore, a transponder that is attached toan add/drop port of the multiplexer/de-multiplexer circuit pack 1520,can forward and receive wavelengths from either of the two degrees ofthe ROADM circuit pack. Because of this, the add/drop ports are referredto as directionless add/drop ports—meaning the add drop ports are notdedicated to a particular direction of the optical node. If two ROADMcircuit packs 1510 a-b are paired to form a four degree optical node (asshown in 1600 of FIG. 16A), wherein ROADM circuit packs 1510 a-b areidentical to ROADM circuit pack 1510), the optical couplers 1555 and1556 allow a transponder that is attached to an add/drop port of themultiplexer/de-multiplexer circuit pack 1520 to forward and receivewavelengths from any of the four degrees of the combined two ROADMcircuit packs 1510 a and 1510 b. The wavelength equalizers (1505 a, 1505e, 1505 f, and 1505 j) on the two ROADM circuit packs are used to steerthe added and dropped wavelengths to and from each degree byappropriately blocking or passing wavelengths. Therefore, the wavelengthequalizers are said to perform directionless steering for the add/dropports.

Additionally, the wavelength equalizers (1505 b-e and 1505 g-j) on thetwo ROADM circuit packs 1510 a-b are used to select which wavelengthsfrom the Line input interfaces and add ports are allowed to exit a givenoutput interface (degree), by appropriately blocking or passingwavelengths.

FIG. 16A shows a four degree optical node 1600. It uses two of the ROADMcircuit packs 1510 a and 1510 b, and a single multiplexer/de-multiplexercircuit pack 1520. The single multiplexer/de-multiplexer circuit pack1520 contains two WDM input ports (IN1 1575 b and IN2 1575 a), and twoWDM output ports (OUT1 1575 d and OUT2 1575 c), allowing both the ROADMcircuit packs to share a common set of transponders (attached to theadd/drop ports on the multiplexer/de-multiplexer circuit pack). Thecommon set of transponders can connect to any of the four degrees (East1672 b, West 1672 a, North 1672 d, and South 1672 c). ROADM circuit Pack1 1510 a sends all wavelengths it receives from its two line interfaces1672 a-b to ROADM circuit Pack 2 1510 b via ROADM circuit Pack 1's twoExpress Out ports (1 & 2 1674 a-b). Similarly, ROADM circuit Pack 2 1510b sends all wavelengths it receives from its two line interfaces 1672c-d to ROADM circuit Pack 1 1510 a via ROADM circuit Pack 2's twoExpress Out ports (1 & 2 1678 a-b). The result is that both ROADMCircuit Pack 1 1510 a and Circuit Pack 2 1510 b have access to allwavelengths received from all four degrees of the optical node.

In 1600, Express OUT1 1674 a, Express OUT2 1674 b, Express IN1 1677 a,and Express IN2 1677 b, correspond to the same signals Express OUT1 1560a, Express OUT2 1560 d, Express IN1 1560 b, and Express IN2 1560 c in1500 respectively. Similarly, in 1600, Express OUT1 1678 a, Express OUT21678 b, Express IN1 1676 a, and Express IN2 1676 b, correspond to thesame signals Express OUT1 1560 a, Express OUT2 1560 d, Express IN1 1560b, and Express IN2 1560 c in 1500 respectively.

FIG. 16B shows a four degree optical node 1650. It uses two of the ROADMcircuit packs 1510 a-b, and two multiplexer/de-multiplexer circuit packs1420 a-b. (Alternatively, it could also use multiplexer/de-multiplexercircuit packs 1520, and just use only one pair of IN/OUT ports.) Usingtwo multiplexer/de-multiplexer circuit packs provides some addedreliability. A drawback is that a given transponder attached to anadd/drop port of one of the multiplexer/de-multiplexer circuit packswill only be able to communicate through the two optical degreesassociated with the ROADM that the multiplexer/de-multiplexer circuitpack is attached to. So in this case, the add/drop ports aredirectionless, but a given transponder is only able to send and receivewavelengths from two of the four degrees.

The two multiplexer/de-multiplexer circuit packs 1520, 1420 may containactive components (i.e., components requiring electrical power in orderto operate), or they may contain only passive components (athermal AWGs,for example). If the multiplexer/de-multiplexer circuit packs containsonly passive components, then the multiplexer/de-multiplexer circuitpacks could optionally be placed outside of the electrical shelf that isholding the ROADM circuit packs.

FIG. 17 shows a two degree optical node 1700 that is identical to theoptical node 1500, except that a single wavelength equalizing array isused to supply all the required wavelength equalizers needed toconstruct the optical node. (Alternatively, multiple smaller wavelengthequalizing arrays could be utilized.) The wavelength equalizers WE1-WE10in 1700 correspond to the wavelength equalizers WE1-WE10 in 1500. Thesingle wavelength equalizing array 310 may be identical to thewavelength equalizing array 310 discussed in reference to FIG. 3.

A single ROADM circuit pack 1710 supplies all the required opticalcircuitry to support two optical degrees, including input and outputamplifiers for each degree, an optical common port connectable to aplurality of directionless add/drop ports, optical supervisory channelcircuitry (not shown), optical channel monitoring (not shown), and asingle wavelength equalizing array 310 that is used to both selectwavelengths for each degree and to perform directionless steering forthe add/drop ports.

The ROADM circuit pack can be used as a stand-alone ROADM in a twodegree node, or it can be paired with a second identical ROADM circuitpack in order to form a four degree node. The four Express ports(Express Out 1 & 2 1760 a,d and Express In 1 & 2 1760 b,c) are used tointerconnect the two ROADMs in the same manner as shown in FIG. 16A.

As can be seen in 1700, a single multiplexer/de-multiplexer circuit pack1720 is used to add and drop wavelengths to/from the Line 1 1701 a-b andLine 2 1702 a-b interfaces. Therefore, a transponder that is attached toan add/drop port of the multiplexer/de-multiplexer circuit pack 1720,can forward and receive wavelengths from either of the two degrees ofthe ROADM circuit pack. If a second ROADM circuit pack is added to theoptical node, a transponder that is attached to an add/drop port of themultiplexer/de-multiplexer circuit pack 1720, can forward and receivewavelengths from any of the four degrees of the resulting optical node.The wavelength equalizers on the ROADM circuit pack are used to steerthe added and dropped wavelengths to and from each degree byappropriately blocking or passing wavelengths. Therefore, the wavelengthequalizers are said to perform directionless steering for the add/dropports for each degree.

Additionally, the wavelength equalizers on the ROADM circuit pack 1710are used to select which wavelengths from the Line input interfaces areallowed to exit a given output Line interface (degree), by appropriatelyblocking or passing wavelengths.

The ROADM circuit pack is constructed on one or more printed circuitboards that are bound together electrically and mechanically so that thecircuit pack can be plugged into a backplane as a single entity. TheROADM circuit pack additionally contains a front panel (used to housethe optical connectors associated with the optical ports on the ROADM),electrical control circuitry (used to take in user commands needed tocontrol the ROADM), power supply circuitry (used to provide the variousvoltage levels and electrical currents needed to power the variouscomponents on the ROADM), and one or more backplane connectors (neededto connect electrical signals on the ROADM to signals on the back planethat the ROADM card is plugged into).

Alternatively, the optical multiplexer/de-multiplexer circuitry on themultiplexer/de-multiplexer circuit pack 1720 could be placed on theROADM circuit pack 1710, thus eliminating a circuit pack in the opticalnode.

The add/drop ports on the multiplexer/de-multiplexer circuit pack 1720are considered to be colored add/drop ports. This is because eachadd/drop port is used to support a particular optical frequency(wavelength). So therefore, add/drop port 1 will only support wavelengthfrequency 1, and therefore a transponder attached to add/drop port 1must only generate wavelength frequency 1. An alternative (not shown) isto supply an alternative multiplexer/de-multiplexer circuit pack thatcontains colorless add/drop ports. A colorless add/drop port can be usedto support any of the r wavelength frequencies associated with the ROADMcircuit pack, and therefore a transponder attached to add/drop port 1 isallowed to generate any of the r wavelength frequencies.

The wavelength equalizing array saves physical space and electricalpower by utilizing common optics and electronics for all the wavelengthequalizers in the array, thus making it more suitable for compactedge-of-network applications. The single wavelength equalizing arrayalso provides a means to simplify the construction of the ROADM circuitpack that it is placed upon.

In summary, this invention presents an embodiment of an optical node1600 comprising of four optical degrees, and further comprising of aplurality of directionless add/drop ports 1561, 1560, and including afirst circuit pack 1510 a and a second circuit pack 1510 b, wherein eachcircuit pack interfaces to at least two of the four optical degrees 1672a-d. The node additionally contains at least one wavelength equalizingarray 310. The optical node 1600 may further include a third circuitpack 1520/1720, containing the plurality of directionless add/drop ports1561, 1560, and wherein the first and second circuit packs 1510 a-bdirect wavelengths to and from the third circuit pack. The first andsecond circuit packs may be ROADM circuit packs, each comprising of asingle wavelength equalizing array and a common port connectable to aplurality of directionless add/drop ports, wherein each ROADM circuitpack interfaces to at least two of the four optical degrees, and whereineach wavelength equalizing array is used to both select wavelengths forthe optical degrees and to perform directionless steering for theplurality of directionless add/drop ports.

FIG. 18 shows a two degree optical node 1800 that is identical to theoptical node 1500, except that a single wavelength equalizing array 600is used to supply all the required wavelength equalizers needed toconstruct the optical node. The wavelength equalizing array that is usedis the wavelength equalizing array that was described in reference toFIG. 6. This wavelength equalizing array can be configured to performthe function of multiple 1 by 2 WSS devices. Therefore, the function ofthe optical coupler 1534 of optical node 1500 is additionally absorbedwithin the wavelength equalizing array 600. Also, the functions ofoptical couplers 1531 and 1533 are partially absorbed within the array600 in 1800. The 2 by 1 WSS function 1840 a performs the function of WE11505 a, WE6 1505 f, and optical coupler 1534 within optical node 1500,while the 2 by 1 WSS function 1840 b performs the function of WE2 1505b, WE3 1505 c, and partially optical coupler 1531 within optical node1500, and the 2 by 1 WSS function 1840 c performs the function of WE71505 g, WE8 1505 h, and partially optical coupler 1533 within opticalnode 1500, and the 2 by 1 WSS function 1840 d performs the function ofWE4 1505 d, WE5 1505 e, and partially optical coupler 1531 withinoptical node 1500, and the 2 by 1 WSS function 1840 e performs thefunction of WE9 1505 i, WE10 1505 j, and partially optical coupler 1533within optical node 1500. As can be seen from the figure, using thewavelength equalizing array 600 in place of wavelength equalizing array310 further simplifies the ROADM circuit pack due to its additionallevel of integration.

Although a wavelength equalizing array of 2 by 1 WSS devices wasutilized to build ROADM circuit pack 1800, a wavelength equalizing arraythat can be configured for either 4 by 1 WSS devices or 2 by 1 WSSdevices could be used instead, in order to eliminate additionalcircuitry. For instance, a first 4 by 1 WSS could absorb WE2 1505 b, WE31505 c, WE4 1505 d, WE5 1505 e, and coupler 1531 on the ROADM circuitpack 1500. Similarly, a second 4 by 1 WSS could absorb WE7 1505 g, WE81505 h, WE9 1505 i, WE10 1505 j, and coupler 1533 on the ROADM circuitpack 1500. A 2 by 1 WSS could absorb WE1 1505 a, WE6 1505 f, and coupler1534 on the ROADM circuit pack 1500. Therefore, different ROADM circuitpacks can be constructed such that they are built using a singlewavelength equalizing array wherein different size WSS functions areutilized within the array.

In general, an optical node or ROADM circuit pack could be constructedusing a wavelength equalizing array that can be partitioned into anarray of k₁1×1, k₂1×2, k₃1×3 . . . , k_(p)1×p wavelength selectiveswitches, where p is any integer number greater than 1, and k_(j) is anyinteger value greater than or equal to 0. A single type of wavelengthequalizing array could be used to build different types of ROADM circuitpacks. For instance, wavelength equalizing array 350 (FIG. 3) could beused to build a two-degree ROADM circuit pack 1010, a three-degree ROADMcircuit pack 1310, or a four-degree capable ROADM circuit pack 1710.Similarly, wavelength equalizing array 800 (FIG. 8) could be used tobuild a two-degree ROADM circuit pack 1110, a three-degree ROADM circuitpack 1410, or a four-degree capable ROADM circuit pack 1810.

Although in 1800 two ROADM circuit packs are required to construct afour degree optical node, all four degrees can be placed on a singleROADM circuit pack. In order to build the four degree ROADM using asingle ROADM circuit pack, a wavelength equalizing array of 20wavelength equalizers would be required—five for each of the fourdegrees. Alternatively, two wavelength equalizers with 10 wavelengthequalizers each could be used.

Additionally, optical nodes containing greater than four degrees couldbe constructed by extending the concepts used to construct the three andfour degree nodes.

FIG. 19 shows a two degree optical node 1900 that is identical to theoptical node 1700, except that two additional wavelength equalizingarrays 1990 a-b are used to support optical channel monitor functions.As shown in FIG. 19, an additional 1 to 2 coupler 1991 & 1992 has beenadded after the output of each of the two output amplifiers within ROADMcircuit pack 1910. The couplers are used to send a portion of the lightfrom each output amplifier to the wavelength equalizers 1990 a-b.Operationally, each of the two newly added wavelength equalizers 1990a-b are used to cycle through all r wavelengths exiting the two lineinterfaces in order to measure the optical power of each wavelengthusing photo diodes 1994 a-b.

FIG. 20 shows a two degree optical node 2000 that is similar to theoptical node 1000, except that u−6 internal transponders 2057 a-b areintegrated in the ROADM circuit pack 2010 (wherein u may be any integervalue greater than six). A wavelength equalizing array 380 with uwavelength equalizers is used. Each additional wavelength equalizerbeyond six is used to filter out a single wavelength that is thendropped to an integrated transponder. Four optical couplers 2046-2049are added to the node of 1000. Coupler 2048 is a (u−6): 1 coupler usedto combine the output wavelengths from the u−6 internal transponders.Coupler 2047 is used to combine the wavelengths from the internaltransponders with the wavelengths from the multiplexer (via common port2070 b) within the multiplexer/de-multiplexer circuit pack 2020. Anoptical amplifier (not shown) could optionally be placed at the outputof optical coupler 2047. Optical coupler 2035 is then used to broadcastthe wavelengths from the internal transponders and from themultiplexer/de-multiplexer circuit pack to both degrees—allowing thewavelengths from the internal transponders to be directionless.

In the drop direction, new coupler 2046 is used to broadcast all thedropped wavelengths received from both degrees to both themultiplexer/de-multiplexer circuit pack (via common port 2070 a) and tocoupler 2049. Coupler 2049 is a 1: (u−6) coupler used to broadcast allthe dropped wavelengths received from both degrees to the u−6 wavelengthequalizers that are used to filter wavelengths for the u−6 internaltransponders.

A ROADM circuit pack with integrated transponders 2010 allows forespecially compact optical nodes, as no external transponders arerequired for cases where a small numbers of wavelengths are added anddropped.

FIG. 21 shows a three degree optical node 2100 that is similar to theoptical node 1300, except that u−12 internal transponders are integratedin the ROADM circuit pack 2110 (wherein u may be any integer valuegreater than twelve). A wavelength equalizing array 380 with uwavelength equalizers is used. Each additional wavelength equalizerbeyond twelve is used to filter out a single wavelength that is thendropped to an integrated transponder. Four optical couplers 2146-2149are added to the node of 1300. Coupler 2148 is a (u−12): 1 coupler usedto combine the output wavelengths from the u−12 internal transponders2157 a-b. Coupler 2147 is used to combine the wavelengths from theinternal transponders with the wavelengths from the multiplexer withinthe multiplexer/de-multiplexer circuit pack 2120. An optical amplifieris optionally placed at the output of optical coupler 2147. Opticalcoupler 2135 is then used to broadcast the wavelengths from the internaltransponders and from the multiplexer/de-multiplexer circuit pack to allthree degrees—allowing the wavelengths from the internal transponders tobe directionless.

In the drop direction, new coupler 2146 is used to broadcast all thedropped wavelengths received from all three degrees to both themultiplexer/de-multiplexer circuit pack 2120 (via common port 2170 a)and to coupler 2149. Coupler 2149 is a 1: (u−12) coupler used tobroadcast all the dropped wavelengths received from all three degrees tothe u−12 wavelength equalizers that are used to filter wavelengths forthe u−12 internal transponders.

FIG. 22 shows an expandable (to four degrees) two degree optical node2200 that is similar to the optical node 1700, except that u−10 internaltransponders are integrated in the ROADM circuit pack 2210 (wherein umay be any integer value greater than ten). A wavelength equalizingarray 380 with u wavelength equalizers is used. Each additionalwavelength equalizer beyond ten is used to filter out a singlewavelength that is then dropped to an integrated transponder. Fouroptical couplers 2246-2249 are added to the node of 1700. Coupler 2248is a (u−10): 1 coupler used to combine the output wavelengths from theu−10 internal transponders. Coupler 2247 is used to combine thewavelengths from the internal transponders with the wavelengths from themultiplexer within the multiplexer/de-multiplexer circuit pack 2220. Anoptical amplifier is optionally placed at the output of optical coupler2247. Optical coupler 2235 is then used to broadcast the wavelengthsfrom the internal transponders and from the multiplexer/de-multiplexercircuit pack to both degrees on the circuit pack—allowing thewavelengths from the internal transponders to be directionless withrespect to the two degrees on the circuit pack.

In the drop direction, new coupler 2246 is used to broadcast all thedropped wavelengths received from both degrees on the circuit pack toboth the multiplexer/de-multiplexer circuit pack (via common port 2270a) and to coupler 2249. Coupler 2249 is a 1: (u−10) coupler used tobroadcast all the dropped wavelengths received from both degrees to theu−10 wavelength equalizers that are used to filter wavelengths for theu−10 internal transponders.

A drawback of the optical node 2200 is that the u−10 internaltransponders can only send to and receive from the two degrees of thecircuit pack that they reside on. Optical node 2300 in FIG. 23 overcomesthis limitation. The u−12 internal transponders 2357 a-b within ROADMcircuit pack 2310 can send and receive to and from any of the fourdegrees when two ROADM circuit packs 2310 are paired together to form afour degree node. This is accomplished by using an additional four-fiberinterconnection between the two paired ROADM circuit packs. In FIG. 23the four additional signals that are passed between the two ROADMcircuit packs are labeled: Internal Add Out 2380 a, Internal Add In 2380d, Internal Drop Out 2380 c, and Internal Drop In 2380 b. Four opticalcouplers are added to the ROADM circuit pack 2210: 2375-2378. Coupler2375 is used to broadcast the composite signal from coupler 2348containing the generated wavelengths from all u−12 internal transpondersto both optical coupler 2376 and Wavelength Equalizer WE11 (2305 a).Wavelength Equalizer WE11 (2305 a) is used to block or pass any of theinternally generated wavelengths to the paired ROADM circuit pack (thesecond ROADM circuit pack). This is a useful feature if an internallygenerated wavelength of a particular frequency is already being injectedon the paired ROADM circuit pack. The output of WE11 (2305 a) is sent tothe optical connector labeled Internal Add Out 2380 a on the first ROADMcircuit pack. Internal Add Out 2380 a on the first ROADM circuit pack isconnected to Internal Add In on the second ROADM circuit pack via anoptical jumper, and vice versa. The wavelengths arriving on the opticalconnector labeled Internal Add In on the second ROADM circuit pack areforwarded to the optical coupler 2376 on the second ROADM circuit pack,where they are combined with the internal generated wavelengths of thesecond circuit pack. Therefore, the signal exiting coupler 2376 containsthe internally generated wavelengths of the second ROADM circuit pack,and any internally generated wavelengths from the first ROADM circuitpack that will be forwarded to at least one of the two degrees of thesecond ROADM circuit pack. All of these wavelengths are then combinedwith the wavelengths from the multiplexer/de-multiplexer circuit pack2320 using optical coupler 2347. The resulting signals are optionallyamplified by the ADD Amp 2211, and then broadcasted to both WE10 (2305b) and WE5 (2305 c). WE10 (2305 b) is used to pass or block wavelengthsto Line Out 2 (2302 b), while WE5 (2305 c) is used to pass or blockwavelengths to Line Out 1 (2301 b). Therefore, it can be seen thatinternally generated wavelengths from the first ROADM circuit pack canbe forwarded to both degrees of the paired second ROADM circuit pack.

In the drop direction, wavelengths to be dropped from the Line In 1(2301 a) and Line In 2 (2302 a) interfaces on the first ROADM circuitpack are selected via WE1 (2305 d) and WE6 (2305 e). These two sets ofwavelengths to be dropped are combined using coupler 2334. The compositeWDM signal from 2334 is broadcasted to optical coupler 2378 and theoptical connector labeled Internal Drop Out 2380 c using optical coupler2377. All of the dropped signals from the first ROADM circuit pack aresent to the second ROADM circuit pack via the optical connector labeledInternal Drop Out 2380 c on the first ROADM circuit pack. The opticalconnector labeled Internal Drop Out 2380 c on the first ROADM circuitpack is connected to the optical connector labeled Internal Drop In onthe second ROADM circuit pack using an optical jumper. Therefore, allthe dropped wavelengths from the first ROADM circuit pack are madeavailable to the second ROADM circuit pack via the connector labeledInternal Drop In on the second ROADM circuit pack. The wavelengthsarriving on the connector labeled Internal Drop In on the second ROADMcircuit pack are forwarded to Wavelength Equalizer WE12 (2305 f) on thesecond circuit pack. WE12 (2305 f) can be used to block any wavelengthsthat are not being dropped on the second ROADM circuit pack. Typically,WE12 (2305 f) should block all wavelengths other than the wavelengthsdestined for internal transponders on the second ROADM circuit pack. Thewavelengths that are not blocked by WE12 (2305 f) are combined with thewavelengths being dropped from the Line 1 (2301 a) and Line 2 (2302 a)interfaces on the second ROADM circuit pack using coupler 2378 on thesecond ROADM circuit pack. The combined signals are optionally amplifiedby the Drop Amp 2312 on the second ROADM circuit pack, and thenbroadcasted to both the multiplexer/de-multiplexer circuit pack 2320 andoptical coupler 2349 via coupler 2346. Coupler 2349 broadcasts itsinputted signal to the entire group of the u−12 Wavelength Equalizersused to filter out individual drop wavelengths for the internaltransponders on the second ROADM circuit pack. In this manner,wavelengths dropped from any of the four degrees in a four degree nodecan be forwarded to any internal transponder on either of the two pairedROADM circuit packs (assuming all wavelength blocking is accounted for).The two wavelength equalizers WE11 (2305 a) and WE12 (2305 f) can beused to isolate the add/drop signals associated with the paired ROADMcircuit packs.

The optical node 2400 with wavelength equalizing array 350 shown in FIG.24 is an alternative to optical node 2300. In the optical node 2400, theinternal transponders can send and receive wavelengths from any of thefour degrees when a four degree node is created using two of the ROADMcircuit packs 2410, but instead of the internal transponders beinglocated within the ROADM circuit packs they are instead located withinthe multiplexer/de-multiplex circuit pack 2420. This greatly simplifiesthe design, but a separate wavelength equalizing array 380 is nowrequired in the node for the multiplexer/de-multiplex circuit pack. Inthe add direction, the output from u number of transponders are combinedusing optical coupler 2448. The composite WDM signal from coupler 2448is then combined with the composite WDM signal from the multiplexer(MUX) via coupler 2447. The resulting signal is optionally amplified bythe Add Amp 2411, and then broadcasted to both ROADM circuit packs (onlyone shown) attached to the multiplexer/de-multiplex circuit pack 2420.In this manner, any signal generated by the transponders internal to themultiplexer/de-multiplex circuit pack 2420 are able to be inserted intoeither of the two degrees on the two ROADM circuit packs (via WE5 (2405b) and WE10 (2405 a)).

In the drop direction, wavelengths being dropped from both Line In 1(2401 a) and Line In 2 (2402 a) on a given ROADM circuit pack arecombined using coupler 2434, and then forwarded to themultiplexer/de-multiplex circuit pack 2420. Coupler 2495 is then used tocombine dropped signals from both ROADM circuit packs into one compositeWDM signal that is amplified by the Drop Amp 2412 and then broadcastedto both the DMUX and optical coupler 2449 via coupler 2446. Coupler 2449is used to broadcast all of the dropped channels from both ROADM circuitpacks to all of the u wavelength equalizers within the wavelengthequalizing array 380. Each of the u wavelength equalizers is used toselect a single wavelength for its corresponding internal transponder2457 a-u. Therefore, in this manner, each of the u internal transpondershas access to all of the dropped wavelengths associated with all fourdegrees.

Although only a single common optical port is shown on the ROADM circuitpacks of the optical nodes 1000, 1300, 1700, 1900, 2000, 2100, 2200,2300, 2400, and 2500, the invention is not limited to a single commonport on a given ROADM circuit pack, and in fact, a given ROADM circuitpack may contain any number of common ports C. Each common port requirestwo wavelength equalizers per degree, with one of the two wavelengthequalizers being used in the drop direction, and with one of the twowavelength equalizers being used in the add direction—each wavelengthequalizer being used in the same manner as was shown for the ROADMcircuit packs containing only a single common port.

In order to provide additional flexibility and reliability, the opticalamplifiers within an optical node may be pluggable into the front panelof a ROADM circuit pack, as illustrated in FIG. 25 and FIG. 26. FIG. 252500 shows a ROADM circuit pack 2510 with wavelength equalizing array200 with five front panel pluggable amplifiers 2501 a-e. There are fourpluggable amplifiers 2501 a-d containing a single EDFA 2502 a-d, and onepluggable amplifier containing two EDFAs 2501 e. Each pluggableamplifier may contain the amplifying EDFA and other electrical andoptical components (not shown). Each pluggable amplifier may furthercomprise of an electrical connector (not shown), used to applyelectrical power to the amplifier, as well as control signals to controlthe amplifier and retrieve status information from the amplifier. Eachpluggable amplifier may additionally comprise of an optical connector2506 a-f used to attach an external optical transmission fiber, and anoptical connector 2503 a-f used to optically jumper 2504 a-f theassociated amplifier to other optical circuitry 2530-2535 within theROADM circuit pack via optical connector 2505 a-f. Optionally, theoptical jumper 2504 a-f could be replaced by a blind-mate opticalconnector on the pluggable amplifier.

FIG. 26 (2600) shows a three-dimensional view of the ROADM circuit pack2610 that can accommodate the five pluggable amplifiers 2501 a-e shownin 2500. FIG. 26 shows three pluggable amplifiers 2601 a-c (eachcomprising of a single EDFA) plugged into the front panel 2650 of theROADM circuit pack 2610. FIG. 26 also shows a pluggable amplifier 2601 e(comprising of a two EDFAs) plugged into the front panel 2650 of theROADM circuit pack 2610. Additionally, FIG. 26 shows a fifth pluggableamplifier 2601 d external to the ROADM circuit pack. Pluggable amplifier2601 d may be plugged into slot 2630 on the front panel 2650 of theROADM circuit pack 2610. Each of the pluggable circuit packs 2601 a-dcontaining a single EDFA also comprises of an optical connector 2606 a-dto attach an external optical transmission fiber, and an opticalconnector 2603 a-d used to optically jumper the associated amplifier toother optical circuitry within the ROADM circuit pack via opticalconnectors 2605 a-d contained on the front panel 2650 of the ROADMcircuit pack 2610. The pluggable circuit pack 2601 e containing a twoEDFAs also comprises of optical connectors 2606 e-f to attach externaloptical transmission fibers, and an optical connector 2603 e-f used tooptically jumper the associated amplifier to other optical circuitrywithin the ROADM circuit pack via optical connectors 2605 e-f containedon the front panel 2650 of the ROADM circuit pack 2610. The opticaljumper used to connect the pluggable amplifier to the other opticalcircuitry within the ROADM circuit pack may comprise of a substantiallyflat planer lightwave circuit with optical connectors 2680, or it maycomprise of some alternative optical connection technology (such as asimple short optical cable). The jumper 2680 could be further fastenedto the front panel 2650 using some mechanical means such as mechanicalscrews 2690 a-b.

FIG. 27 illustrates a process 2700 of constructing a multi-degreeoptical node utilizing a wavelength equalizing array. At block 2701, thenumber of degrees N for the optical node is selected. At block 2705, thenumber of ports C common to all degrees is selected. At Step 2710, a setof N−1+C wavelength equalizers is allocated for the purpose oftransmission of wavelengths from the first optical degree. At block2715, a decision is made: if there are additional optical degrees, theprocess returns to block 2710, where an additional set of N−1+Cwavelength equalizers is allocated for each additional degree. Once allN degrees have a set of N−1+C wavelength equalizers allocated to them,the process proceeds to block 2720. At this point, the total number ofwavelength equalizers allocated is: N×(N−1+C). At block 2720, it isdetermined if there is at least one common optical port within themulti-degree optical node. If there are no common ports, the processproceeds to block 2730. If there is at least one common port, then theprocess proceeds to block 2725. At block 2725, for each common port, aset of N wavelength equalizers is allocated for transmission of a set ofwavelengths from each common port. The number of wavelength equalizersallocated at this block is: C×N. Once the wavelength equalizers havebeen allocated for the common ports, the process proceeds to block 2730.At block 2730, it is determined if there are any optical channelmonitors. If there are no optical channel monitors, then the processproceeds to block 2740. If there is at least one optical channelmonitor, then at block 2735, M number of wavelength equalizers areallocated for M number of optical channel monitors. It should be notedthat two or more optical degrees may share a single optical channelmonitor by switching the optical channel monitor between the two or moreoptical degrees. Once the M wavelength equalizers have been allocated,the process proceeds to block 2740. At block 2740, it is determined ifthere are any embedded transponders. If there are no embedded opticaltransponders, then the process ends. If there is at least one embeddedtransponder, then at block 2745, T number of wavelength equalizers areallocated for T number of embedded transponders. Once, the T number ofwavelength equalizers have been allocated at block 2745 the processends. When the process 2700 ends, the total number of wavelengthequalizers allocated to the optical node is: N×(N−1+C)+(C×N)+M+T, whichis equal to N²+N(2C−1)+M+T. For the special case where C=1, the totalnumber of wavelength equalizers allocated is equal to: N²+N+M+T.

Based upon the process presented in 2700, it is seen that the inventionprovides for a method of constructing a multi-degree optical nodeutilizing a wavelength equalizing array, comprising of allocating afirst set of wavelength equalizers 2710 for selection of a first set ofwavelengths for transmission from a first optical degree, and allocatingat least a second set of wavelength equalizers 2710 for selection of atleast a second set of wavelengths for transmission from at least asecond optical degree, wherein the number of optical degrees Ncomprising the node is used to determine the number of wavelengthequalizers assigned to each set. The method further includes allocatingan additional set of wavelength equalizers 2725 for selection of anadditional set of wavelengths for transmission from a common portconnectable to a plurality of directionless add/drop ports. The methodfurther includes allocating at least one wavelength equalizer 2735 forselection of wavelengths for an optical channel monitor. The method alsofurther includes allocating at least one wavelength equalizer 2745 forselection of a wavelength for at least one transponder.

In the foregoing description, the invention is described with referenceto specific example embodiments thereof. It will, however, be evidentthat various modifications and changes may be made thereto withoutdeparting from the broader spirit and scope of the present invention.The specification and drawings are accordingly to be regarded in anillustrative rather than restrictive sense.

What is claimed is:
 1. An optical node, comprising: at least two opticaldegrees; an optical channel monitoring function; a first circuit packconnectable to the at least two optical degrees and comprising at leasta first wavelength equalizing array; and a second circuit packcomprising a plurality of directionless add/drop ports and at least asecond wavelength equalizing array, wherein the at least firstwavelength equalizing array is used to select wavelengths for the atleast two optical degrees, and to perform directionless steering ofwavelengths to and from the plurality of directionless add/drop portsand to provide wavelength filtering for the optical channel monitoringfunction.
 2. The optical node of claim 1, further comprising at leastone transponder.
 3. The optical node of claim 1, wherein the firstcircuit pack includes at least one transponder.
 4. The optical node ofclaim 1, wherein the second circuit pack includes at least onetransponder.
 5. The optical node of claim 1, further comprising outputoptical amplification for the at least two optical degrees.
 6. Theoptical node of claim 1, further comprising input optical amplificationfor the at least two optical degrees.
 7. The optical node of claim 1,wherein the second circuit pack includes at least one optical amplifier.8. A ROADM circuit pack, comprising: at least two optical degrees; anoptical channel monitoring function; at least one transponder; and atleast one wavelength equalizing array, used to select wavelengths forthe at least two optical degrees, and to provide wavelength filteringfor the optical channel monitoring function, and to provide wavelengthselection for the at least one transponder.
 9. The ROADM circuit pack ofclaim 8, further comprising a common port connectable to a plurality ofdirectionless add/drop ports.
 10. The ROADM circuit pack of claim 9,wherein the at least one wavelength equalizing array is used to performdirectionless steering of wavelengths to and from the plurality ofdirectionless add/drop ports.
 11. The ROADM circuit pack of claim 8,further comprising a plurality of directionless add/drop ports.
 12. TheROADM circuit pack of claim 11, wherein the at least one wavelengthequalizing array is used to perform directionless steering ofwavelengths to and from the plurality of directionless add/drop ports.13. The ROADM circuit pack of claim 8, further comprising output opticalamplification for the at least two optical degrees.
 14. The ROADMcircuit pack of claim 8, further comprising input optical amplificationfor the at least two optical degrees.
 15. The ROADM circuit pack ofclaim 8, further comprising a drop optical amplifier.
 16. The ROADMcircuit pack of claim 8, further comprising an add optical amplifier.17. The ROADM circuit pack of claim 8, comprising a single wavelengthequalizing array.
 18. A method of constructing a multi-degree opticalnode utilizing a wavelength equalizing array, comprising: allocating atleast one wavelength equalizer for selection of wavelengths for anoptical channel monitor; allocating at least one wavelength equalizerfor selection of a wavelength for at least one transponder; andallocating a first set of wavelength equalizers for selection of a firstset of wavelengths for transmission from a common port connectable to aplurality of directionless add/drop ports.
 19. The method of claim 18,further comprising allocating at least a second set of wavelengthequalizers for selection of at least a second set of wavelengths fortransmission from a first optical degree.
 20. The method of claim 19,further comprising allocating at least a third set of wavelengthequalizers for selection of at least a third set of wavelengths fortransmission from a second optical degree.